I would like the ability to make a common field a unique field like the e-mail address is currently. As an example, our Association uses a unique State issued ID number as an identifier. We would like to be sure that two people don't enter the same number by accident.
Andrew Steele commented
Our association uses a unique ID number issued by another organization. Many of our members do not have email, so it would be useful to check that this custom field is unique.